Process and apparatus for building tires for vehicle wheels

ABSTRACT

A process and an apparatus for building tires for vehicle wheels wherein the process includes the step of assembling components of elastomeric material on a forming support, in which at least one of the components of elastomeric material is manufactured by the steps of: i) dispensing a continuous elongated element of elastomeric material; ii) applying the continuous elongated element in the form of coils disposed in side by side relationship or at least partly superposed, wound up on the forming support, so as to form the at least one component of elastomeric material of the tire; iii) exerting a first pressure on a central region of a portion of the continuous elongated element applied onto the forming support; and iv) exerting a second pressure on side regions of the portion of the continuous elongated element applied onto the forming support.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase application based onPCT/IB2010/052659, filed Jun. 15, 2010, which claims the priority ofItalian Application No. MI2009A001238, filed Jul. 13, 2009, and thebenefit of U.S. Provisional Application No. 61/213,848, filed Jul. 21,2009, the content of all of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process and an apparatus for buildingtires for vehicle wheels.

2. Description of the Related Art

A tire for vehicle wheels generally comprises a carcass structureincluding at least one carcass ply having respectively opposite endflaps in engagement with respective annular anchoring structures,integrated into the regions usually identified as “beads”.

Associated with the carcass structure is a belt structure comprising oneor more belt layers, located in radially superposed relationship witheach other and with the carcass ply and provided with textile ormetallic reinforcing cords having a crossed orientation and/or beingsubstantially parallel to the circumferential extension direction of thetire.

A tread band is applied at a radially external position to the beltstructure, which tread band is made of elastomeric material like othersemifinished products constituting the tire.

Respective sidewalls of elastomeric material are further applied at anaxially external position to the side surfaces of the carcass structure,each extending from one of the side edges of the tread band until closeto the respective annular anchoring structure to the beads.

After building of the green tire by assembly of respective semifinishedproducts, a vulcanization and molding treatment is generally carriedout, which aims at determining the structural stabilization of the tireby cross-linking of the elastomeric compounds and also at impressing thetread band, wound up around the carcass before vulcanization, with adesired tread pattern and the region close to the tire sidewalls withpossible distinctive graphic marks.

Within the present description and in the following claims, by“elastomeric material” it is intended a composition including at leastone elastomeric polymer and at least one reinforcing filler. Preferably,this composition further comprises additives such as cross-linkingagents and/or plasticizers. Due to the presence of the cross-linkingagents, this material can be cross-linked by heating, so as to form thefinal article of manufacture.

Document WO 2009/040534 in the name of the same Applicant, discloses aprocess for manufacturing tires for vehicle wheels, which processcomprises the steps of: building the carcass structure of a green tireon a first forming drum in at least one carcass-building line, buildinga crown structure on a second forming drum in at least onecrown-building line, shaping the carcass structure into a toroidalconformation, while it is being assembled to the crown structure in atleast one assembly and shaping station. The assembly and shaping stationis synchronized with the carcass-building line and the crown-buildingline. Each carcass structure is associated with the respective firstforming drum on which it is built up to the end of the assembly andshaping step. The above mentioned stations are operatively associatedwith units adapted to supply elementary semi-finished products, such ascontinuous elongated elements of elastomeric material, strips ofelastomeric material containing two or more textile or metallic cords,individual textile or metallic of coated with elastomeric material. Oncethe careen tire has been built, it is cured and molded in at least onevulcanization and molding line separated from the building line. In theabove described work stations, said elementary semi-finished productscan be wound up into coils disposed in side by side relationship and/orat least partly superposed, such as in the case of the continuouselongated elements for example, contributing to formation of the liner,under-liner, under-layers, fillers present in the regions of the beads,sidewalls, tread band.

In this regard, document EP 1 375 118 discloses a green tire, or a tirecomponent, that is manufactured by winding into coils and rolling arubber strip on a building drum. To this aim, a building devicecomprises a rigid support or building drum, on which the rubber strip iswound into coils and rolled, an extruder adapted to extrude the rubberstrip, a winder for winding the rubber strip on the rigid support, and aflattening roller, adapted to flatten the projection of a step portionproduced by a first part of the rubber strip and a second part of thesame rubber strip overlapping the first one. Flattening prevents theresidual air from remaining entrapped during vulcanization, in theregions close to the step portions between the outer surface of the tirecomponent and the vulcanization mold and avoids the consequent presenceof hollows and slits in the finished tire. The surface of the flatteningroller is provided with a knurl. The step of spirally winding androlling the rubber strip and the flattening step can be carried outsimultaneously.

Document EP 1 754 592 discloses a method of building a tire, said methodallowing elimination of the residual air between the step portions of anoverlapped portion of a tire component and the vulcanization mold, so asto avoid formation of hollows, slits, etc. causing a reduction in thetire lifetime. The method comprises the steps of flattening a stepformed at an overlapped portion of a tire component and optimizing thecross-section shape of said overlapped portion. The apparatus used forputting this method into practice comprises a building platform, anextruder for extrusion of a rubber strip and a pressure roller. Acomponent of the tire is formed by spirally winding the rubberribbon-like strip, extruded through the extruder, on the buildingplatform and forming an overlapped portion of this rubber strip. A stepof this overlapped portion that is exposed on the outer surface of thetire component is flattened under pressure through the pressure rollerthat is such disposed as to face the building platform by a specificangle relative to the extension direction of the rubber strip and isheated to the plasticization temperature in order to make the outer tiresurface smooth.

SUMMARY OF THE INVENTION

The Applicant has noticed that, in addition to the air entrapped betweenthe steps defined by the rubber strip and the cavity of thevulcanization mold, as described in documents EP 1 754 592 and EP 1 375118 mentioned above, also air pockets or more generally gas pockets areformed under the continuous elongated element of elastomeric materialalready during laying of said element into at least partly superposedcoils. During vulcanization, since the radially outermost (tread band)and radially innermost (the liner, for example) surface layers that arecured the first acquire imperviousness features, the air contained inthese pockets remains entrapped therein or moves to the outer surfacebut does not escape therefrom, thus forming surface bubbles.

The Applicant has further noticed that the higher the laying temperatureof the continuous elongated element is, the more important the justdescribed phenomenon concerning formation of air pockets is, and thatsaid temperature increases on increasing of the laying speed, or ondecreasing of the time intervening between ejection of the compound ofthe continuous elongated element from the extruder and application ofsaid element into coils on the respective forming drum.

The Applicant has therefore ascertained that this phenomenon isparticularly significant in the processes for manufacturing tires forvehicle wheels like that described in the above mentioned document WO2009/040594 in which the individual floor to floor times necessary forbuilding the different tire portions such as the crown structure (beltstructure and tread band) and carcass structure must be reduced to theminimum for obtaining high production rates.

The Applicant has perceived that by exerting pressure in adifferentiated manner on the elongated element just laid, the airpossibly entrapped between portions of the elongated element at leastpartly overlapping each other can escape easily and in a more efficientmanner, avoiding the persistent presence of air pockets that cangenerate the above mentioned drawbacks.

The Applicant has finally found that, by exerting pressure on a centralregion of a portion of the continuous elongated element immediatelyafter laying of same and by subsequently exerting pressure on the sideregions of the same portion, it is possible to discharge the airpossibly entrapped under said continuous elongated element and thereforeavoid said air forming pockets and bubbles that would remain entrappedin the cured and molded tire.

More specifically, in a first aspect, the present invention relates to aprocess for building tires for vehicle wheels comprising the step of:assembling components of elastomeric material on a forming support, inwhich at least one of said components of elastomeric material is made bythe steps of:

i) dispensing a continuous elongated element of elastomeric material;

ii) applying the continuous elongated element in the form of coilsdisposed in side by side relationship or at least partly superposed,wound up on the forming support in order to form said at least one tirecomponent of elastomeric material;

iii) exerting a first pressure on a central region of a portion of thecontinuous elongated element applied onto the forming support;

iv) exerting a second pressure on side regions of said portion of thecontinuous elongated element applied onto the forming support.

It is the Applicant's opinion that the first pressure directs its forceagainst the continuous elongated element squashing and pressing it inthe middle, laterally moving the possible air bubbles entrapped thereby,while the second pressure spreads and smoothes the continuous elongatedelement on its sides forcing said air bubbles to the outside.

In accordance with a second aspect, the present invention relates to atire for vehicle wheels built following the process as described and/orclaimed.

In a third aspect, the present invention relates to an apparatus forbuilding tires for vehicle wheels comprising: at least one formingsupport; at least one assembly device for assembling components ofelastomeric material on the forming support; wherein said at least oneassembly device comprises: at least one dispensing device for dispensinga continuous elongated element of elastomeric material; at least oneapplication device for applying said continuous elongated element in theform of coils disposed in side by side relationship or at least partlysuperposed, wound up on the forming support, and forming said at leastone component of elastomeric material of the tire; at least one pressuredevice operatively acting on an applied portion of the continuouselongated element; wherein the pressure device comprises a centralroller and two side rollers, each laterally offset relative to thecentral roller and on the opposite side relative to the other sideroller.

The present invention, in at least one of the above aspects can have oneor more of the preferred features as hereinafter described.

Preferably step iv) follows step iii).

In this way, the pressure exerted on the central region moves possibleair bubbles from the center to the sides of the continuous elongatedelement while, subsequently, pressures exerted on the side regions causeescape of the entrapped air from the side edges.

Preferably, between step ii) and step iii) a first time intervalintervenes which is included between about 0 s and about 1 s.

In addition, preferably, between step iii) and step iv) a second timeinterval intervenes which is included between about 0 s and about 1 s.

The shorter the time intervening between distribution, application andcompression of the continuous elongated element is, the greater thetemperature and plasticity of the elastomeric material during thecompression steps, and consequently the greater the ease with which thecompound is deformed and molded.

In addition, preferably, during steps iii) and iv), said portion has anaverage temperature included between about 90° C. and about 110° C.

In a preferred alternative embodiment, along a direction orthogonal tothe longitudinal extension of the continuous elongated element, the sideregions are partly superposed on the central region according to asuperposition width.

Preferably said superposition width is included between about 0.5 mm andabout 5 mm.

Said superpositions ensure that pressure is exerted over the wholesurface of the continuous elongated element so as to eliminate thepersistent presence of underlying air bubbles.

In a preferred alternative embodiment of the process, during step iv)the second pressure is exerted on at least one side edge of thecontinuous elongated element.

In addition, preferably, during step iv), said at least one side edge issubmitted to a hammering action.

By “hammering” it is intended application of micro-hits on the surfaceof the continuous elongated element, carried out by means of at leastone roller for example, which is provided with a side work surfacehaving raised elements and/or grooves (knurling),

Pressure exerted on the edge and hammering have a visual effect on theouter and visible components of the tire such as the tread band andsidewalls for example, because they squash the continuous elongatedelement wound into coils and create microfractures therein, so that theseparation lines between adjacent coils become less visible also aftervulcanization.

Preferably, step ii) is carried out at a linear application speed of thecontinuous elongated element included between about 0.1 m/s and about 2m/s.

Compression of the continuous elongated element after application ofsame takes a fundamental importance for high application speeds, asthose stated above, that are necessary for obtaining high productionvolumes. In fact, corresponding to the high speeds are high layingtemperature to which the phenomena of air expansion and bubblegeneration are more important and frequent.

In a preferred alternative embodiment of the apparatus, the centralroller has a rotation axis distinct from a rotation axis of the siderollers.

Preferably, along an application direction, the central roller isinterposed between the application device and the two side rollers.

This structure allows pressure to be first exerted in the middle andsubsequently on the side regions of the continuous elongated element.

Preferably, along an application direction, a first distance between theapplication device and the central roller is included between about 20mm and about 200 mm.

Preferably, along an application direction, a second distance betweenthe central roller and the two side rollers is included between about 10mm and about 100 mm.

Since the application device too preferably comprises an applicatorroller, these distances are intended measured between the contact pointsof the applicator roller and the rollers of the pressure device with thecontinuous elongated element applied onto the forming support.

Said distances must preferably be maintained within the stated limitsfor two reasons.

First of all, for compressing the continuous element when the compoundis still very hot (the smaller the distance is, the shorter the timeintervening between application and compression), for the alreadyhighlighted reasons; and in addition, for limiting a misalignmentbetween the center line of the application device and the center line ofthe pressure device. In fact the continuous elongated element isspirally wound on the forming support according to a determinedspiraling angle, measured between a longitudinal extension direction ofthe continuous elongated element and a plane orthogonal to the rotationaxis of the forming support. Misalignment between the center line of theapplication device and the center line of the pressure device and, asregards the individual pressure device, misalignment between the centerline of the central roller and the center line of the side rollers allowthe just laid portion of the continuous elongated element to becorrectly compressed. These misalignments that should be set at eachlaying cycle with suitable adjustment mechanisms based on the concernedgeometries and speeds, can be neglected if the above mentioned distancesare of rather small value.

According to a preferred embodiment, a peripheral work surface of thecentral roller at least partly faces at least one of the peripheral worksurfaces of the side rollers.

Preferably, along a direction parallel to rotation axes of the centralroller and side rollers, the peripheral work surface of the centralroller has a superposition width with said at least one of theperipheral work surfaces of the side rollers included between about 0.5mm and about 5 mm.

The relative position between the rollers ensures that the whole surfaceof the continuous elongated element is submitted to pressure.

According to a preferred embodiment, the central roller and each of theside rollers are movable irrespective of each other along a directionsubstantially orthogonal to the forming support.

Preferably, the pressure device comprises spring elements operativelyassociated with the central roller and the two side rollers, to maintainsaid rollers into contact with said portion of the continuous elongatedelement.

In addition, preferably, each of the spring elements is associated withone of the rollers in a manner independent of the others.

In addition, preferably, the spring elements are pneumatic cylinders.

Contact between each of the rollers and the continuous elongated elementis ensured under any laying condition and for every speed and layingangle.

According to a preferred embodiment, the pressure device comprises: asupporting frame and a central small arm having a central portionthereof hinged thereon.

Preferably said central small arm carries the central roller on a firstend thereof.

Preferably the pressure device further comprises a first spring elementmounted on the supporting frame and secured to a second end of thecentral small arm.

More preferably, said pressure device comprises two side small armspositioned on opposite sides of the central small arm, each having acentral portion thereof hinged on the supporting frame and carrying oneof the side rollers on a first end thereof.

In a further preferred alternative solution, said pressure devicecomprises two second spring elements, each mounted on the supportingframe and secured to a second end of a respective side small arm.

The specific structure adopted is of simple and cheap structure and atthe same time stiff and reliable, so as to ensure a correct and preciselaying and pressing of the continuous elongated element.

According to a preferred embodiment, the assembly device comprises ahead supporting the application device and pressure device.

Alignment between the application device and pressure device is ensuredby the fact that they are mounted as a single assembly.

Preferably, the central roller has a peripheral contact edge having aradius of curvature in diametrical section that is included betweenabout 0.5 mm and about 3 mm.

Preferably, each of the two side rollers has a peripheral contact edgehaving a radius of curvature in diametrical section included betweenabout 0.5 mm and about 3 mm.

In addition, preferably, the diametrical section of each of the two siderollers is asymmetric and said peripheral contact edge is the externalone.

Said radius of curvature and the position of the peripheral edge aresuch selected as to exert a predetermined pressure at a predeterminedpoint of the continuous elongated element.

Preferably, a peripheral work surface of the central roller has a widthincluded between about 3 mm and about 10 mm.

Preferably, a peripheral work surface of each of the side rollers has awidth included between about 3 mm and about 10 mm.

Preferably, the side rollers have a minimum distance from each otherincluded between about 3 mm and about 10 mm.

Preferably, the central roller has a maximum diameter included betweenabout 20 mm and about 80 mm.

Preferably, each of the side rollers has a maximum diameter includedbetween about 20 mm and about 80 mm.

The geometry and sizes of the rollers enable compression of the wholesurface of the continuous elongated element to be compressed and alsothe steps defined by the superposed adjacent coils to be flattened, thushelping in eliminating the traces of the elongated element on the treadband and/or the sidewalls of the cured and molded tire.

Also helping in this second function is a peripheral work surface of thecentral roller and of each of the side rollers having raised elementsfor exerting a hammering action on the portion of the continuouselongated element.

Further features and advantages will become more apparent from thedetailed description of a preferred but not exclusive embodiment of anapparatus for building tires for vehicle wheels in accordance with thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

This description will be set out hereinafter with reference to theaccompanying drawings, given by way of non-limiting example, in which:

FIG. 1 is a diagrammatic top view of a plant for tire productioncomprising an apparatus for building tires in accordance with thepresent invention;

FIG. 2 is a diagrammatic side view of an assembly device being part ofthe apparatus in question and comprising a pressure device in accordancewith the present invention;

FIG. 3 shows an enlarged portion of the assembly device seen in FIG. 2;

FIG. 4a is a side view of the pressure device seen in FIG. 2;

FIG. 4b is a front view of the pressure device seen in FIG. 2;

FIG. 5 shows an enlarged portion of the pressure device in FIG. 4b witha forming support carrying a continuous elongated element already laidand spaced apart from the pressure device, for the sake of clarity;

FIG. 5a is a diagrammatic plan view showing rollers of the pressuredevice acting on the continuous elongated element;

FIG. 6 is a diagrammatic diametrical section of a tire for vehiclewheels obtained with the plant seen in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the drawings, a plant for tire production comprisingan apparatus 2 for building tires in accordance with the presentinvention has been generally identified with reference numeral 1.

Plant 1 is intended for manufacturing tires 3 (FIG. 6) essentiallycomprising at least one carcass ply 4 preferably internally coated witha layer of airtight elastomeric material or a so-called “liner”, twoso-called “beads” 6 integrating respective annular anchoring structures7 possibly associated with elastomeric fillers 7 a and in engagementwith the circumferential edges of the carcass ply 4, a belt structure 8applied to the carcass ply 4 at a radially external position, a treadband 9 applied to the belt structure 8 at a radially external position,in a so-called crown region of the tire 3, and two sidewalls 10 appliedto the carcass ply 4 at laterally opposite positions, each at a sideregion of the tire 3, extending from the corresponding bead 6 to thecorresponding side edge of the tread band 9.

Apparatus 2 for building tires preferably comprises a line for buildingcarcass structures 11, in which a carcass structure comprising at leastone of the carcass plies 4 and the annular anchoring structures 7 isformed on a first forming drum 12′. Denoted in FIG. 1 are a plurality ofwork stations 13 belonging to said line 11 for building carcassstructures and each dedicated to formation and/or application of acomponent of elastomeric material of tire 3 on the first forming drum12′. The first forming drum 12′ is sequentially transferred from onestation to the following one, by means of robotized arms, not shown, orother suitable devices.

By way of example, in a first station 13 liner 5 is made through windingof a continuous elongated element of elastomeric material into coilsdisposed mutually in side by side relationship and/or at least partlysuperposed and distributed along the forming surface of the firstforming drum 12′. In at least one second station 13 manufacture of oneor more carcass plies 4 can be carried out, which carcass plies areobtained by laying strip-like elements on the first forming drum 12′, incircumferentially approached relationship, said strip-like elementsbeing formed by cutting to size a continuous strip of elastomericmaterial comprising textile or metallic cords disposed parallel in sideby side relationship. A third building station 13 can be dedicated tointegration of the annular anchoring structures 7 with said at least onecarcass ply 4, through application of said annular anchoring structures7 at an axially external position to the flaps of said at least onecarcass ply 4 knocked down in the direction of the rotation axis of saidfirst forming drum 12′, which flaps will be subsequently turned uparound the annular anchoring structures 7.

Apparatus 2 for building tires further comprises a line for buildingcrown structures 14, in which a crown structure comprising at least thebelt structure 8 and tread band 9 is formed on a second forming drum12″. Denoted in FIG. 1 is a plurality of work stations belonging to saidline 14 for building crown structures and each dedicated to formingand/or applying a component of elastomeric material of tire 3 on thesecond forming drum 12″. The second forming drum 12″ is sequentiallytransferred from one station to the subsequent one, by means ofrobotized arms, not shown, or other suitable devices.

At least one building station 15 can be dedicated to manufacture of theannular belt structure 8 obtained by laying strip-like elements incircumferentially approached relationship, which strip-like elements areobtained by cutting to size a continuous strip of elastomeric materialcomprising preferably metallic mutually parallel cords, and/or bywinding a textile or metallic rubberized reinforcing cord into axiallyapproached coils, in the crown portion of tire 3. By way of example, awork station 15 can be intended for manufacture of the tread band 9 orsidewalls 10. Tread band 9 and sidewalls 10 are preferably obtained bywinding of at least one continuous elongated element of elastomericmaterial into mutually approached and/or at least partly superposedcoils.

Apparatus 2 is further provided with an assembly and conformationstation 16 operatively associated with line 11 for building carcassstructures and line 14 for building crown structures. In the assemblyand conformation station 16 the carcass structure is shaped andassociated with the crown structure, so as to obtain a green tire.

Tires built by apparatus 2 are sequentially transferred to avulcanization unit line 17 integrated into plant 1 from which cured andmolded tires 3 are obtained.

As mentioned above, in accordance with the present invention, at leastone of the components of only elastomeric material of tire 3, such asliner 5, fillers 7 a and/or other parts of elastomeric material of beads6, sidewalls 10, tread band 9, underliner, underbelt layer, underlayerof the tread band, abrasion-proof elements and/or others, is obtained byan assembly device denoted as a whole at 18 (FIG. 2).

The assembly device 18 comprises a dispensing device in the preferredform of an extruder (not shown), producing a continuous elongatedelement 19 of elastomeric material. The extruder is provided with acylinder into which elastomeric material is introduced. The cylinderheated to a controlled temperature, just as an indication includedbetween about 60° C. and about 100° C., operatively houses a rotatingscrew, by effect of which the elastomeric material is pushed along saidcylinder to an outlet orifice of the extruder.

Through the outlet orifice, the continuous elongated element 19 isdispensed at a desired linear speed, corresponding to a so-called“target value” of the volumetric flow rate, just as an indicationincluded between about 10 cm³/s and about 60 cm³/s, and at a temperaturejust as an indication included between about 90° C. and about 110° C.

An application device 20, operating downstream of the extruder, carriesout application of the continuous elongated element 19 coming from theextruder, onto a forming support 12. The forming support 12 can be saidfirst forming drum 12′ or said second forming drum 12″.

During application, the forming support 12, supported in overhanging byone of said robotized arms for example, is driven in rotation andsuitably moved in front of the application device 20 for distributingthe continuous elongated element 19 into approached and/or at leastpartly superposed coils, wound around such a forming support 12, so asto form liner 5 for example, or any other component of elastomericmaterial of the tire being processed.

The application device 20 comprises (FIG. 2) at least one roller orother applicator member 21 acting in thrust relationship towards theforming support 12, for instance by effect of a pneumatic actuator 22,for applying the continuous elongated element 19 onto the formingsupport 12 itself.

Operatively interposed between the extruder and the application device20 is a conveyor 23, the function of which consists in bringing thecontinuous elongated element 19 coming out of the extruder onto theforming support 12 and until the application device 20.

In the preferred embodiment herein illustrated, the conveyor 23comprises a conveyor belt 24 defined by a cogged rubber belt or a metalbelt, passing over rollers 24 a, 24 b. The conveyor belt 24 on the upperpart has a forward stretch supporting the elongated element 19.

The continuous elongated element 19 coming out of the conveyor belt 24at the end roller 24 a is continuously laid on support 12 by theapplicator roller 21. In particular, the applicator roller 21 pressesthe continuous elongated element 19 sliding under and against it,against the forming support 12 for determining adhesion of same. Theapplicator roller 21 therefore rotates in the opposite directionrelative to rotation of the forming support 12.

Downstream of the applicator member 21 there is a pressure device 27which is preferably mounted on a head 28 also carrying the applicationdevice 20. The applicator member 21 and pressure device 27 are furtheroperatively supported relative to conveyor 23. The head 28 is in factmounted on a structure holding the conveyor 23.

The pressure device 27, better shown in FIGS. 3, 4 a, 4 b and 5,comprises a substantially box-shaped supporting frame 29 formed with anupper wall 30 and a pair of side walls 31 a defining an inverted-Ushape. A bottom wall 31 b connects the two side walls 31 a and issecured to head 28.

Respective fixed arms are secured to lower portions of the side walls 31a, which arms each have a first end 32 a integral with the supportingframe 29 and a second end 32 b. The second ends 32 b of the two fixedarms 32 face each other for supporting a central roller 33 a and twoside rollers 33 b, as described in detail in the following.

In particular, a central small arm 34 is hinged, at a central portionthereof, on the second ends 32 b of the fixed arms 32 around a firstarticulation axis “X-X”. A first end 34 a of the central small arm 34has a fork rotatably carrying the central roller 33 a. E second end 34 bof the central small arm 34, opposite to the first one 34 a, is hingedon a spring element 35 in turn mounted on the supporting frame 29.Preferably, as in the embodiment shown, the spring element 35 is apneumatic cylinder. An end of the pneumatic cylinder 35, belonging tothe rod 35 a of the cylinder 35 itself is hinged on said central smallarm 34 around a second articulation axis “Y-Y” and an opposite end,belonging to the body 35 b of the cylinder 35, is hinged on a bracketintegral with the upper wall 30 of the supporting frame 29.

Two side small arms 36 are positioned on opposite sides of the centralsmall arm 34. The lateral small arms 36 are parallel to each other andcross the central small arm 34. Each of the lateral small arms 36 has acentral portion thereof hinged on the second ends 32 b of the fixed arms32 and on the central small arm 34 around the first articulation axis“X-X”. A first end 36 a of each of the lateral small arms 36 rotatablycarries one of the side rollers 33 b. A second end 36 b of each of thelateral small arms 36, opposite to the first one 36 a, is hinged on arespective spring element 37 in turn mounted on the supporting frame 29.

Preferably, as in the embodiment shown, each of the two spring elements37 is a pneumatic cylinder an end of each of the pneumatic cylinders 37belonging to the rod 37 a of cylinder 37, is hinged on the respectivelateral small arm 36 around a third articulation axis “Z-Z” and anopposite end, belonging to the body 37 b of the cylinder 37, is hingedon a bracket integral with the upper wall 30 of the supporting frame 29.Each of the pneumatic cylinders 37 is associated with one of rollers 33b in a manner independent of the others.

The central roller 33 a, two side rollers 33 b and the applicator roller21 have rotation axes that are substantially parallel to each other. Thecentral roller 33 a is substantially aligned with the applicator roller21 along a trajectory or application direction of the continuouselongated element on the forming support 12. The two side rollers 33 bare coaxial to each other and offset towards opposite sides of thecentral roller 33 a (FIGS. 5 and 5 a).

The central roller 33 a has a rotation axis “A-A” distinct from therotation axis “B-B” of the side rollers 33 b and the rotation axis “C-C”of the applicator roller 21. In particular, along said applicationdirection, the central roller 33 a remains positioned between theapplicator roller 21 and the two side rollers 33 b (FIG. 3).

The central roller 33 a has (FIG. 5a ) a maximum diameter “Da”, intendedas the diameter of the radially outermost portion, included betweenabout 20 mm and about 80 mm. Each of the side rollers 33 b has a maximumdiameter “Db” included between about 20 mm and about 80 mm.

Immediately after laying carried out by the applicator member 21, thecentral roller 33 a exerts a first pressure “P₁” on a central region 38of the just laid portion of the continuous elongated element 19, andsubsequently the two side rollers 33 b exert respective second pressures“P₂” on side regions 39 of the same portion (FIGS. 5 and 5 a). Thecentral 33 a and side 33 b rollers roll against the continuous elongatedelement 19, that has already adhered to the forming support 12 androtate in opposite ways relative to the rotation direction of saidforming support 12.

Downstream of the pressure device 27, therefore, the continuouselongated element 19 laid on the forming support 12 has a central stripcompressed by the central roller 33 a and two side strips compressed bythe side rollers 33 b (FIG. 5a ).

The pneumatic cylinders 35, 37 push rollers 33 a, 33 b against thecontinuous elongated element 19 and, through the central small arm 34and lateral small arms 36, maintain rollers 33 a, 33 b in contact withthe continuous elongated element 19. Due to the described structure, thecentral roller 33 a and each of the side rollers 33 b are movableindependently of each other along a direction substantially orthogonalto the peripheral surface of the forming support 12.

The portion of the continuous elongated element 19 that has just comeout of the extruder and has been submitted to said pressures “P₁”, “P₂”,has an average temperature “t_(m)” substantially equal to or not muchlower than the exit temperature and preferably included between about90° C. and about 110° C.

Distance “d₁” between the rotation axis “C-C” of the applicator roller21 and the rotation axis “A-A” of the central roller 33 a is preferablyincluded between about 20 mm and about 200 mm. Distance “d₂” between therotation axis “A-A” of the central roller 33 a and the rotation axis“B-B” of the side rollers 33 b is preferably included between about 10mm and about 100 mm (FIGS. 3 and 5 a).

As a result, a first distance “ΔS₁” measured along the applicationdirection between the application device 20 and central roller 33 a,intended as the distance measured between the contact point of theapplicator roller 21 with the continuous elongated element 19 and thecontact point of the central roller 33 a with the continuous elongatedelement 19, is included between about 20 mm and about 220 mm.

A second distance “ΔS₂” measured along the application direction betweenthe central roller 33 a and the two side rollers 33 b, intended as thedistance measured between the contact point of the central roller 21with the continuous elongated element 19 and the axis passing by the twocontact points between the side rollers 33 b and the continuouselongated element 19, is included between about 10 mm and about 110 mm.

The periods of time intervening between the action of the applicatorroller 21, the action exerted by the central roller 33 a and the actionexerted by the side rollers 33 b on the same portion of continuouselongated element 19 depend on the above stated distances and the linearapplication speed “V” that is preferably included between about 0.1 m/sand about 2 m/s, more preferably between about 0.5 m/s and about 1.5m/s.

Between laying of a portion of the continuous elongated element 19 andthe pressing action carried out by the central roller 33 a on the sameportion there is a first time interval “ΔT₁” included between about 0 sand about 1 s. In addition, between the pressing action carried out bythe central roller 33 a and the pressing action carried out by the twoside rollers 33 b there is a second time interval “ΔT₂” included betweenabout 0 s and about 1 s.

In the embodiment shown, the peripheral work surface 40 a of the centralroller 33 a has, in diametrical section, an arched and symmetricperipheral contact edge (FIGS. 5 and 5 a) which has a radius ofcurvature “r_(a)” preferably included between about 0.5 mm and about 3mm. Also the peripheral work surface 40 b of each of the side rollers 33b is arched and symmetric (FIG. 5) and has a radius of curvature “r_(b)”preferably included between about 0.5 mm and about 3 mm.

In accordance with an alternative embodiment not shown, said peripheralwork surface 40 b of each of the side rollers 33 b is asymmetric and theedge in contact with the continuous elongated one 19 is the outer edge.

In the embodiment shown in the accompanying drawings, the peripheralwork surface 40 a of the central roller 33 a partly faces the peripheralwork surfaces 40 b of the two side rollers 33 b. In other words, in afront view as the one in FIG. 5, the peripheral work surface 40 a of thecentral roller 33 a is partly superposed on the peripheral work surfaces40 b of both the side rollers 33 b. The facing or superposition widths“Δ1 a”, measured along a direction parallel to the rotation axes of therollers, are included between about 0.5 mm and about 5 mm.

Width “La” of the peripheral work surface 40 a of the central roller 33a is included between about 3 mm and about 10 mm. Width “Lb” of theperipheral work surface 40 b of each of the side rollers 33 b isincluded between about 3 mm and about 10 mm.

In addition, the two side rollers 33 b are mutually spaced apart by aminimum distance “d_(m)”, measure parallel to the rotation axes,included between about 3 mm and about 10 mm.

The central roller 33 a and each of the side rollers 33 b act on acommon region of the continuous elongated element 19. As a result, thecontinuous elongated element 19 has two parallel bands compressed bothby the central roller 33 a and the side rollers 33 b (FIG. 5a ). Thecentral region 38 and side regions 39 and, consequently, the aforesaidcentral strip and side strips are partly superposed at said bandsaccording to superposition widths “Δls” preferably included betweenabout 0.5 mm and about 5 mm.

Due to the width and position of the side rollers 33 b, the side edges41 of the continuous elongated element 19 are compressed and preferablyalso squashed through an hammering action. To this aim, preferably, theperipheral work surface 40 a, 40 b of the central roller 33 a and/or ofthe side rollers 33 b has a knurling defining raised elements 41delimiting corresponding grooves.

Alternatively, smooth rollers are used on softer and adhesive compoundsfor example, where surface working of the rollers could cling to thecontinuous elongated element of elastomeric material.

The invention claimed is:
 1. A process for building a tire for a vehiclewheel comprising: assembling components of elastomeric material on aforming support, wherein at least one of said components of elastomericmaterial is manufactured by the steps of: i) dispensing a continuouselongated element of elastomeric material in a form of a strip; ii)applying, by way of an application roller, a portion of the continuouselongated element in a form of coils disposed at least partly superposedin a radial direction of the forming support, wound on the formingsupport so as to form said at least one component of elastomericmaterial of the tire; iii) exerting, by way of a central roller distinctfrom the application roller, a first pressure on a central region of oneof the coils of the portion of the continuous elongated element afterapplying the continuous elongated element onto the forming support; andiv) exerting, by way of two side rollers each laterally offset towardopposite sides of the central roller, a second pressure only on sideregions of said one of the coils of said portion of the continuouselongated element applied onto the forming support, the side regionsbeing disposed on opposing sides of the central region, wherein step iv)follows step iii), wherein the continuous elongated element has across-sectional shape, measured perpendicular to a dispensing direction,comprising a width that is greater than a height, the height beingmeasured perpendicular to an application surface of the forming supportat a point where the portion is brought into contact with theapplication surface, and wherein the cross-sectional shape of thecontinuous elongated element is filled continuously with material,wherein the central roller and each of the side rollers are movableirrespective of each other along a direction orthogonal to the formingsupport at a point where the portion is brought into contact with eachrespective roller, wherein the central roller is carried by a centralsmall arm hingedly connected to fixed arms about a first articulationaxis, wherein the fixed arms are secured to a supporting frame, whereinan end of the central small arm, opposite to the central roller, isconnected to the supporting frame by a first spring element, wherein theside rollers are carried by lateral small arms each laterally offsettoward opposite sides of the central small arm, wherein the lateralsmall arms are hingedly connected to the fixed arms about the firstarticulation axis, and wherein an end of each of the lateral small arms,opposite to the respective side roller of each lateral small arm, isconnected to the supporting frame by a respective second spring element.2. The process as claimed in claim 1, wherein a first time intervalbetween 0 s and 1 s intervenes between step ii) and step iii).
 3. Theprocess as claimed in claim 1, wherein a duration of time between 0 sand 1 s intervenes between step iii) and step iv).
 4. The process asclaimed in claim 1, wherein during steps iii) and iv), said portion hasan average temperature between about 90° C. and about 110° C.
 5. Theprocess as claimed in claim 1, wherein, along a direction orthogonal tothe longitudinal extension of the continuous elongated element, the sideregions are partly superposed on the central region according to asuperposition width.
 6. The process as claimed in claim 5, wherein saidsuperposition width is between 0.5 mm and 5 mm.
 7. The process asclaimed in claim 1, wherein during step iv), a hammering action isexerted on the continuous elongated element.
 8. The process as claimedin claim 1, wherein step ii) is carried out at a linear applicationspeed of the continuous elongated element between 0.1 m/s and 2 m/s. 9.The process as claimed in claim 1, wherein, along an applicationdirection, a first distance between a contact point of the applicationroller and the continuous elongated element and a contact point of thecentral roller and the continuous elongated element is between about 20mm and about 200 mm.